Residuum coking and cracking



Oct. 13, 1953 H. z. MARTIN 2,655,465 RESIDUUM COKING AND CRACKING FiledJuly 24, 1951 Hus GAS To FRACTI OHATOK A @Mcram i 'm-1% l L OH. FEEDSeuss Mlxsl MD Sewn/wok Patented Oct. 13, 1953 UNITED STATES PATENTOFFICE 2,655,465 RESIDUUM COKING AND CRACKING Homer Z. Martin, Cranford,N. J., assignor to Standard Oil Development Company, a corporation ofDelaware Application July 24, 1951, Serial No. 238,286

' Claims. (01. 19s-49 This invention relates to a method for cokingferior to that obtained in the more common types and cracking heavyresidual stocks. It relates of catalytic conversion. Also, theinvestment particularly to a method wherein ash and coke costs in theprevious process have been undeforming constituents of a heavy residuumfeed sirably high. are first removed from the feed by being deposited 5It is the main object of the present invention on particles of fluidizedinert solids, preferably to avoid the aforementioned disadvantages bycoke, under conditions conducive to a minimum designing a processrequiring a minimum number conversion of the feed to lighterhydrocarbons, of vessels, having a more economical heat bal- Whileoverall conversion of the feed is primarily ance, a minimum of coke andcatalyst contaminaaccomplished thereafter in a catalytic manner. tion,and a maximum yield of high quality motor Specifically, the vaporsresulting from the coking fuel fractions. Other objects will be apparentzone are passed to a cracking zone containing a from the subsequentdescription of the novel deposit. A characteristic feature of theinvention heavy hydrocarbon feed is contacted with hot catalyst andreheated inerts are segregated. prior particle size distributionsubstantially different to being separately recycled to the appropriatefrom the particle size distribution of the seed conversion zones. coke,a catalyst regeneration step wherein the Various combinations of fluidcoking and carbonaceous deposit formed around the catalyst ing would becondensed and fractionated to proing mixture of solids is separated byeiutriation vide a feed cut which had to be revaporized in or the likeinto its two principal components, the the catalytic cracking step. Theheat requirecatalyst being returned to the catalytic cracking continualfeeding of a heat carrying medium illustrated by a specific examplewherein referby combustion of similarly valuable extraneous ing to whichthe cracking zone containing a dense coking processes, coke and acracking catalyst imposed over a coking zone containing a dense bed ofrelatively coarse coke in a single reactor tain a scouring action on thereactor walls, or ected into the coke bed from which theresulttamination of the coke product by the added reheated cokeparticles are returned to the coking became badly contaminated by theash constitucatalytic cracking zone.

' Referring now in detail to the drawing, re-

duce crude such as an 8% bottoms fraction of quality of the desiredproduct was generally inabout 10-30 Conradson carbon, of about 5 APIgravity and obtained from the vacuum distillation of a West Texas crudeor a similar heavy residue is supplied to coking zone 2 through line Ias a liquid at a temperature of about 300 to 850 F., or preferably atabout 700 F. Petro leum coke particles having a particle size in therange between about 100 and 500 microns, or other inert solids sized sothat little if any is entrained out of the coking zone, are maintainedin the coking zone at a temperature of about 850 F. to 1100 F.,preferably 950 to 1025 EL, as a dense, turbulent, fluidized bed 3 havingan upper level A and an apparent density of about to 50 lbs/cu. ft. withdensities of about 0.01 to 5 lbs/cu. it. above level 4, while an inertgas such as steam introduced through lines and 31 is being passedupwardly through the coke particles at a linear superficial velocity ofabout 0.5 to 5 feet per second.

The vapors produced in the hot coking zone 2 are passed therefromthrough perforated plate 5 into the superimposed catalytic cracking zone6 maintained at about 900 F. to 1000 F. and containing a dense,turbulent, fluidized bed l of a cracking catalyst such as one of theknown synthetic silica-alumina composites. The physical characteristicsof catalyst bed I are essentially similar to those of the coke bed 3described above, except that the catalyst particle size is within therange of about 5 crons and is preferably at least 20 to 5'0 micronssmaller than the smallest particles constituting a substantial portionof the coke in bed 3, so as to assure an efflcient separation of the twosolids in the subsequent elutriation. Thus, for instance, when cokeranging in size down to about 100 microns is used in the coker, thecatalyst particles are preferably in the range between 20 and 50 or 80microns, but when the coke particles of the process range in sizebetween about 200 and 300 microns, catalyst particles in the range up toabout 150 microns may be used. The cracked hydrocarbon vapors arewithdrawn from cracking zone 6 through cyclone 8 or other gas-solidseparator means and passed through line 9 to a conventional finishingsystem for fractionation and recovery of naphtha, gas oil and otherdesired hydrocarbon fractions. The slurry of catalyst in oil withdrawnfrom the bottom of the fractionator may returned to the catalytic bed 6to provide for additional conversion of this heavy part of the overheadproduct. Alternatively, where the quantity of catalyst in thefractionator bottoms is small, or where separation of the catalysttherefrom can be conveniently obtained by sedimentation or otherclarification, it may be preferable to return the bottoms to the cokingzone 2 where some of the high carbon formers will be deposited and asuperior feed is thus provided for the catalytic cracking step.

Spent catalyst is withdrawn from bed I through standpipe it, which mayhave taps H for admitting a small amount of an aeration gas, and thewithdrawn catalyst is finally mixed with air admitted through line l2and passed to regenerator I3 where carbonaceous deposits are burned offthe catalyst in fluid phase at a manner well known per se. Excess heatmay be removed from the system by means of heat exchanger M and hotregenerated catalyst is used to supply the heat requirements of thecoking zone as well as the catalytic cracking zone in the mannerdescribed later herein- Morechanger in a separate vessel through whichhot catalyst is circulated. This allows greater flexibility and controlover regeneration temperature without causing undue coking of feedwithin the heat exhanger, as might otherwise be the case if regeneratortemperature permitted only a low feed circ lation rate through theexchanger when immersed directly in the regenerator bed as shown in thedrawing.

Net coke product may be withdrawn from bed 3 through pipe l8, it beingparticularly desirableto remove those coke particles which have growntoo large for good fluidization in the system. Control of the cokeparticle size in the system can be achieved by screening out the largestcoke particles while recycling the smaller ones, or the withdrawnparticles may even be ground before being returned to the system.However, where grinding is employed, it is desirable to remove also thefines from the coke to be returned, as otherwise such coke fines wouldeventually become mixed with the catalyst and undesirably increase thenecessary amount of carbon burning capacity.

A side stream of coke from coke bed 3 is withdrawn through line H! tomixer-elutriator 20 where the coke particles are mixed with hot catalystparticles withdrawn from regenerator 13 through line 2! while an inertgas such as steam is introduced into the bottom of vessel so throughline 22 at a rate corresponding approximately to the minimumfluidization velocity for the coke particles, i. e. to give a linearsuperficial velocity of about 0.1 to 1 foot per The weight ratio of coketo catalyst being circulated through and mixed in elutriator 20 mayrange between about 0.2 and 3.0. As the two solids become mixed invessel 20, they exchange heat so that the catalyst is cooled and thecoke heated to about 1100 F. and moreover, due to the previouslydescribed difference in particle size, the relatively fine catalyst isstripped from the fluidized mixture in Vessel 20 and entrained to thecatalyst bed 1 in reaction zone 6, thereby supplying the heat requiredby the catalytic conversion step.

Coarse coke particles, essentially free of catalyst and reheated bycontact with the regenerated catalyst, are withdrawn from mixing ves-Sci 2% through standpipe 23 and after admixing with steam from line 3%are returned as a disperse suspension through line 3! to coke bed 3,thereby supplying the necessary heat to the coking reactor. Moreover,especially where a relatively active coke product or a coke of lowervolatile content is desired and where the proc ess produces heat inexcess of its other requirements, it may be preferable to remove netcoke product from the process by way of the hot mixing vessel 20 andstandpipe 24 rather than by way of the somewhat cooler coke bed I! andpipe It described earlier herein.

Having described specific embodiments of the invention as well assuitable methods of operation, it will be understood that this was donefor purposes of illustration rather than limitation. For instance,beyond the scope of the specific example given, the invention is broadlyapplicable to the treatment of heavy residual crude stocks, and offerscertain advantages even with lighter stocks such as cycle stocks or any26622465 other oils which tend to deposit solid residues In the mixingzone, the coke. or other inert such as coke or contaminating ashconstituents solids are reheated to the desired temperature when heatedor cracked Such stocks may be y mixing with about 02 to 3 parts of hotrereduced crudes obtained by atmospheric or vacugenerated catalyst perpart of inerts, the optium distillation and may represent the bottom 5mum ratio in each case obviously depending on 2 to 25 vol. percent ofthe virgincrude distilled, the temperature of the regenerated catalystas or the invention may be applied to heavy clarified well as on thedesired conversion temperatures, oil obtained from catalytic cracking,to tar from oil preheat temperature, etc. a visbreaking operations andto other similar stocks The contact solids in the catalytic cracking orpitches unsuited for direct feeding to a cata- 1 zone may be a catalystsuch as activated clay,

nating propensities. 7

Prior to feeding to the coker, such heavy feed The particle size of thecatalyst may range bestocks are usually preheated to temperatures tween0 to 100, or preferably between and ranging from 200 to 1000 F.,preferably 700 to 80 microns and, as mentioned earlier, the catacarbonfeed may also be diluted in the reaction 24) tion. The apparentdensities and gas velocities in amounts up to about 500 to 5000 cu. ft.per substantially within the same limits as given barrel since suchdiluent gas ofiers a convenient above with reference to the colzersolids, though in transfer lines carrying a dilute suspension lowerthanthe minimum gas velocity required 00f solid particles i v as in li3| of th for the fiuidization of the relatively coarser coker drawing.On the other hand in conversion zones S l dscontaining a dense fluid bedof solids, such as It may also be noted that while the p e e ed in bed 3shown in the drawing, the desired linear embodiments of the inventionuse catalyst in a gas velocity may range between about 0 5 to 5 or ormmore readily entrainable than the inert chosen so as to accomplish thedesired separaand subsequent rejection of the adhered catai well knownper l catalyst by the adhering coke fines. If desired, The inert contactsolids used in the coker are the described invention m be ead y adapt dpreferably coarse coke particles ranging in size to {3111s reverse pe ofpp r on n a man e pumice and t like may similarl be used as fine inertsolids entrained overhead from eel-atriathe coker of some of theaforementioned inorpended in an appropriate inert gas in hydrostitutethe more readily entrainable solid phase 0 m Qumator-heatexchanger may ar id t ranging from about 1 to 150 densed and fractionated beforefeeding into the utes so as to provide sufiicient surface area forcatalytl? crackms'zonethe deposition of a cokable residuum film aroundReactlon condltlons may Include cokmg the solid particles. The ratio ofresiduum feed peratures Of about 809 to 1200 catalytic to solids in thecoker zone is maintained at a cracking temperatures of about 300 to 1009value preferably not in ex f b t; 1 t and catalyst regenerationtemperatures of about wt./hr., when the reactor is operated at about1000 to 1200 F'., depending on the nature of the perature by direct heatexchange with the catalyst before separation and recycling to theconversion zones, are so adjusted as to give the intended temperatureconditions both in the coking zones and the catalytic cracking zones.

Having given a full description of the inven tion and of the manner ofusing. it, the invention is particularly pointed out. and distinctlyclaimed in the appended claims.

I claim:

1. In a process wherein a heavy hydrocarbon feed is first contacted withhot inert solid particles in a coking zone and wherein the resultinghydrocarbon vapors are contacted in a cracking zone with a densefluidized mass of cracking catalyst which has a substantially differentparticle size range than the said inert particles and is subsequentlyregenerated by combustion in a regeneration zone, the improvement whichcomprises mixing hot regenerated catalyst and relatively cool inertsolid particles in a separate heat exchange zone whereby the inertparticles are reheated and the catalyst is cooled, separating thecatalyst from the inert solids by elutriation, returning the reheatedinert solids to the coking zone and returning the cooled catalyst to thecracking zone.

2. A process for converting a heavy hydrocarloOn feed stock into lighterproducts and coke, which comprises contacting the stock in a coking zonewith hot inert solid particles ranging in size up to 500 microns at atemperature between 800 and 1100 F., withdrawing inert solid particlesfrom the coking zone, passing the resulting hydrocarbon vapors upwardlythrough a cracking zone wherein the vapors are contacted at atemperature between 800 and 1l00 F. with a dense turbulent mass offluidized catalyst particles having a particle size range different fromthe particle size range of the inert solid particles, withdrawingproduct hydrocarbons from the cracking zone, withdrawing spent catalystfrom the cracking zone and passing it to a regeneration zone throughwhich an oxygen-containing gas is passed in an upward direction at arate sufficient to maintain the catalyst particles in a dense fluidizedmass at a temperature between 1000 and 1200 F. while carbon is beingburned off withdrawing hot regenerated catalyst particles from theregeneration zone and mixing them in a separate heat-exchange zone withthe inert solid particles withdrawn from the coking zone, separating thecatalyst particles from the reheated inert solids by passing an inertelutriation gas through the particle mixture and passing elutriatedregenerated catalyst particles to the cracking zone, and recycling theseparated, reheated, inert solids to the coking zone for contact withincoming feed stock.

3. A process according to claim 2 wherein the inert solids are cokeparticles of a size between about and 300 microns and wherein thecracking catalyst. particles are of a size. from 0 to 1.00 microns andare at least 20 to 50 microns smaller than the smallest. substantialparticle size fraction of the coke.

4. A process according to claim 2 wherein the catalyst. particles arerelatively coarser than the inert solids.

5. A process for converting a heavy hydrocarbon residuum stock intolighter products and coke, which comprises spraying the stock at about.700 to 850 F. through a dilute vapor phase into a lower dense turbulentcoking bed oi relatively coarse, fluidized inert solid particlesmaintained at about 950 to 1025 F., passing the resulting hydrocarbonvapors upwardly through a dense turbulent bed of relatively fineparticles of cracking catalyst maintained at about 300 to ll00 F.directly above said vapor phase, withdrawing cracked producthydrocarbons from. the catalyst containing zone, also withdrawing spentcatalyst from the turbulent catalyst bed and passing it to aregeneration zone through which an oxygen-containing gas is passed in anupwardly direction. at a rate suflicient to maintain the catalystparticles in a dense fluidized mass at a temperature between 1000 and1200 F. while carbon is being burned off, withdrawing not regeneratedcatalyst particles from the regeneration zone and mixing them in anelutriation zone with inert particles withdrawn from the coking bed,separating the relatively fine catalyst. particles from the relativelycoarse inert particles by passing an inert gas through the particlemixture at a velocity smaller than the minimum entrainment velocity ofthe inert solids but greater than the minimum entrainment velocity ofthe catalyst particles, returning the separated reheated inert solids tothe coking bed and returning the separated catalyst to the catalyticcracking zone.

HOMER Z. MARTIN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,378,531 Becke June 19, 1945 2,388,055 Hemminger Oct. 30,1945 2,421,212 Medlin May 27, 194'! 2,446,247 Scheineman Aug. 3, 1948

5. A PROCESS FOR CONVERTING A HEAVY HYDROCARBON RESIDUUM STOCK INTOLIGHTER PRODUCTS AND COKE, WHICH COMPRISES SPRAYING THE STOCK AT ABOUT700 TO 850* F. THROUGH A DILUTE VAPOR PHASE INTO A LOWER DENSE TURBULENTCOKING BED OF RELATIVELY COARSE, FLUIDIZED INERT SOLID PARTICLESMAINTAINED AT ABOUT 950 TO 1025* F., PASSING THE RESULTING HYDROCARBONVAPORS UPWARDLY THROUGH A DENSE TURBULENT BED OF RELATIVELY FINEPARTICLES OF CRACKING CATALYST MAINTAINED AT ABOUT 800 TO 1100* F.DIRECTLY ABOVE SAID VAPOR PHASE, WITHDRAWING CRACKED PRODUCTHYDROCARBONS FROM THE CATALYST CONTAINING ZONE, ALSO WITHDRAWING SPENTCATALYST FROM THE TURBULENT CATALYST BED AND PASSING IT TO AREGENERATION ZONE THROUGH WHICH AN OXYGEN-CONTAINING GAS IS PASSED IN ANUPWARDLY DIRECTION AT A RATE SUFFICIENT TO MAINTAIN THE CATALYSTPARTICLES IN A DENSE FLUIDIZED MASS AT A TEMPERATURE BETWEEN 1000 AND1200* F. WHILE CARBON IS BEING BURNED OFF, WITHDRAWING HOT REGENERATEDCATALYST PARTICLES FROM THE REGENERA-